MULTI-STAGE REACTION CONTROLLED TEXTURES OF META-TROCTOLITES IN THE BUCK CREEK COMPLEX, NC

The Buck Creek Complex is comprised of metamorphosed mafic and ultramafic rocks located in the Blue Ridge terrane of the Southern Appalachians. The igneous origins of the complex are difficult to resolve through overprinting metamorphic and tectonic events. This study focused on corona textures in metatroctolites, which form the core of the complex with metadunites, for insights into the multi-stage reactions that affected the complex. This investigation helps to shed light onto the range of orogenic, igneous and metamorphic processes that created the Appalachians and the (meta)ultramafic-mafic complexes they contain.

This study investigated the effects of metamorphism on the Buck Creek metatroctolites through combined field analyses, petrography, and scanning electron microscopy. They are principally composed of olivine, plagioclase, orthopyroxene and spinel, igneous textures are absent. Olivine grains in proximity to plagioclase are typically separated by multiple coronas that contain a symplectite layer with intergrowths a few microns wide. The corona textures are comprised of a monomineralic orthopyroxene layer in contact with olivine. This may be followed by monomineralic clinopyroxene and/or spinel layers. A symplectite of clinopyroxene and spinel always occurs in contact with plagioclase.

The olivine and plagioclase are interpreted as relict phases that are indicative of a troctolitic protolith. The corona textures developed during metamorphism as a reaction between olivine and plagioclase. We suggest that diffusion-controlled reactions were important in the development of the multiple coronas. These reactions preserved in the Buck Creek Complex represents the complexity in unravelling the geological history of the Blue Ridge terrane in the Southern Appalachians.